Generally, a starter for a small engine includes a pulley, a cam plate (drive cam), a torque-accumulation spiral spring and a drive gear. The pulley is fixed to a crank shaft of the engine. A centrifugal ratchet is provided on the pulley to be engaged with a cam pawl provided in the cam plate. The drive gear is connected to the cam plate through the torque-accumulation spiral spring.
The drive gear is rotated manually or mechanically (using a sel-motor, for example) to accumulate a rotational torque (energy) in the torque-accumulation spiral spring, thereby starting the engine. When the accumulated rotational torque exceeds a rotational resistance of the engine, the rotational torque accumulated in the torque-accumulation spiral spring is abruptly released to transmit the rotational torque to the crank shaft through the cam plate and the pulley, and the engine is started (for example, see JP-2002-227753-A)
However, the rotational resistance of the engine is not constant. For example, the rotational resistance of the engine becomes highest when a piston is located around an upper dead point, and becomes lowest when the piston is located around a lower dead point.
The rotational resistance of the engine is unstable and changed depending on circumstances. Therefore, when the rotational resistance is low, even before the starting rotational torque (rotational torque necessary for starting the engine) is accumulated in the torque-accumulation spiral spring, the accumulated energy may temporarily (transiently) exceed the rotational resistance to rotate the cam plate. When the cam plate is allowed to be rotated by an insufficiently accumulated energy, since the starting rotational torque cannot be transmitted to the pulley, the engine can not be surely started.